treewide: add license header and enable haslicense linter

Change-Id: I873a8d4082d75e8f813d8a726a41187eea7a065e
Reviewed-on: https://review.monogon.dev/c/monogon/+/3825
Tested-by: Jenkins CI
Reviewed-by: Leopold Schabel <leo@monogon.tech>
diff --git a/osbase/net/dns/forward/up/up.go b/osbase/net/dns/forward/up/up.go
index 9806319..3b208d9 100644
--- a/osbase/net/dns/forward/up/up.go
+++ b/osbase/net/dns/forward/up/up.go
@@ -1,3 +1,6 @@
+// Copyright The Monogon Project Authors.
+// SPDX-License-Identifier: Apache-2.0
+
 // Package up is used to run a function for some duration. If a new function is
 // added while a previous run is still ongoing, nothing new will be executed.
 package up